Localization effect on the metal biosorption capability of recombinant mammalian and fish metallothioneins in Escherichia coli

Equilibrium, kinetic, and thermodynamic studies on the biosorption of lead by human metallothionein gene-cloned bacteria as a novel biosorbent

Heavy metals are the main pollutants in water and are an important global problem that threatens human health and ecosystems. In recent years, there has been an increasing interest in the use of genetically modified bacteria as an eco-friendly method to solve heavy metal pollution problems. The goal of this study was to generate genetically modified Escherichia coli expressing human metallothioneins (hMT2A and hMT3) and to determine their tolerance, bioaccumulation, and biosorption capacity to lead (Pb2+ ). Recombinant MT2A and MT3 strains expressing MT were successfully generated. Minimum inhibition concentrations (MIC) of Pb for MT2A and MT3 were found to be 1750 and 2000 mg L-1 , respectively. Pb2+ resistance and bioaccumulation capacity of MT3 were higher than MT2A. Therefore, only MT3 biosorbent was used in Pb2+ biosorption, and its efficiency was examined by performing experiments in a batch system. Pb2+ biosorption by MT3 was evaluated in terms of isotherms, kinetics, and thermodynamics. The results showed that Pb biosorption fits to the Langmuir isotherm model and the pseudo-first-order kinetic model, and the reaction is exothermic. The maximum Pb2+ capacity of the biosorbent was 50 mg Pb2+ g-1 . The potential of MT3 in Pb biosorption was characterized by Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and scanning transmission electron microscopy (STEM) analyses. The desorption study showed that the sorbent had up to 74% recovery and could be effectively used four times. These findings imply that this biosorbent can be applied as a promising, precise, and effective means of removing Pb2+ from contaminated waters. PRACTITIONER POINTS: In this study, the tolerance levels, bioaccumulation, and biosorption capacities of Pb in aqueous solutions were determined for the first time in recombinant MT2A and MT3 strains in which human MT2A and MT3 genes were cloned. The biosorbent of MT3, which was determined to be more effective in Pb bioaccumulation, was synthesized and used in Pb biosorption. The Pb biosorption mechanism of MT3 biosorbent was identified using isotherm modeling, kinetic modeling, and thermodynamic studies. The maximum Pb removal percentage capacity of the biosorbent was 90%, whereas the maximum biosorption capacity was up to 50 mg Pb2+ g-1 . These results indicated that MT3 biosorbent has a higher Pb biosorption capacity than existing recombinant biosorbents. MT3 biosorbent can be used as a promising and effective biosorbent for removing Pb from wastewater.

Recent advances in bacterial biosensing and bioremediation of cadmium pollution: a mini-review

Cadmium (Cd) pollution has become a global environmental issue because Cd gets easily accumulated and translocated in the food chain, threatening human health. Considering the detrimental effects and non-biodegradability of environmental Cd, this is an urgent issue that needs to be addressed through the development of robust, cost-effective, and eco-friendly green routes for monitoring and remediating toxic levels of Cd. This article attempts to review various bacterial approaches toward biosensing and bioremediation of Cd in the environment. This review focuses on the recent development of bacterial cell-based biosensors for the detection of bioavailable Cd and the bioremediation of toxic Cd by natural or genetically-engineered bacteria. The present limitations and future perspectives of these available bacterial approaches are outlined. New trends for integrating synthetic biology and metabolic engineering into the design of bacterial biosensors and bioadsorbers are additionally highlighted.

Microalgal Metallothioneins and Phytochelatins and Their Potential Use in Bioremediation

The persistence of heavy metals (HMs) in the environment causes adverse effects to all living organisms; HMs accumulate along the food chain affecting different levels of biological organizations, from cells to tissues. HMs enter cells through transporter proteins and can bind to enzymes and nucleic acids interfering with their functioning. Strategies used by microalgae to minimize HM toxicity include the biosynthesis of metal-binding peptides that chelate metal cations inhibiting their activity. Metal-binding peptides include genetically encoded metallothioneins (MTs) and enzymatically produced phytochelatins (PCs). A number of techniques, including genetic engineering, focus on increasing the biosynthesis of MTs and PCs in microalgae. The present review reports the current knowledge on microalgal MTs and PCs and describes the state of art of their use for HM bioremediation and other putative biotechnological applications, also emphasizing on techniques aimed at increasing the cellular concentrations of MTs and PCs. In spite of the broad metabolic and chemical diversity of microalgae that are currently receiving increasing attention by biotechnological research, knowledge on MTs and PCs from these organisms is still limited to date.

Heavy Metal Removal by Bioaccumulation Using Genetically Engineered Microorganisms

Wastewater effluents from mines and metal refineries are often contaminated with heavy metal ions, so they pose hazards to human and environmental health. Conventional technologies to remove heavy metal ions are well-established, but the most popular methods have drawbacks: chemical precipitation generates sludge waste, and activated carbon and ion exchange resins are made from unsustainable non-renewable resources. Using microbial biomass as the platform for heavy metal ion removal is an alternative method. Specifically, bioaccumulation is a natural biological phenomenon where microorganisms use proteins to uptake and sequester metal ions in the intracellular space to utilize in cellular processes (e.g., enzyme catalysis, signaling, stabilizing charges on biomolecules). Recombinant expression of these import-storage systems in genetically engineered microorganisms allows for enhanced uptake and sequestration of heavy metal ions. This has been studied for over two decades for bioremediative applications, but successful translation to industrial-scale processes is virtually non-existent. Meanwhile, demands for metal resources are increasing while discovery rates to supply primary grade ores are not. This review re-thinks how bioaccumulation can be used and proposes that it can be developed for bioextractive applications-the removal and recovery of heavy metal ions for downstream purification and refining, rather than disposal. This review consolidates previously tested import-storage systems into a biochemical framework and highlights efforts to overcome obstacles that limit industrial feasibility, thereby identifying gaps in knowledge and potential avenues of research in bioaccumulation.